1. Field of the Invention
The present invention relates to a range and/or range-and-splitter shift control for a manually shifted, range-type compound transmission. In particular, the present invention relates to an automatic override for a manually shifted, range-type transmission which, at certain vehicle speeds, will prevent inadvertent shifts into prohibited ratios.
2. Description of the Prior Art
Vehicular compound transmissions of the range type, including the combined splitter-and-range type, are well known in the prior art and may be seen by reference to U.S. Pat. Nos. 4,754,665; 5,370,013; 5,737,969 and 5,950,491, the disclosures of which are incorporated herein by reference. Manually shifted, range-type transmissions typically used either a "double-H" type shift pattern wherein range shifting was automatic, or a "repeat-H" type shift pattern wherein the driver is required to manually operate a range selector, usually a button or switch located on the shift knob assembly. Typical "double-H" shift range shift mechanisms may be seen by reference to U.S. Pat. Nos. 5,661,998 and 5,911,787, while typical "repeat-H" shift mechanisms may be seen by reference to U.S. Pat. No. 5,899,121, the disclosures of all of which are incorporated herein by reference. Transmissions with manually or automatically controlled splitter shifting are also known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,435,212 and 6,015,366, the disclosures of which are incorporated herein by reference.
Synchronized transmissions and transmissions utilizing enhanced synchronizers, such as boosted synchronizers, self-engaging synchronizers, double- or triple-cone synchronizers and/or synchronizers activated through various assist mechanisms, are known in the prior art and may be seen by reference to U.S. Pat. Nos. 5,588,516; 5,713,447; 5,738,194 and 5,738,196, the disclosures of which are incorporated herein by reference.
Shift assist systems which include a splitter clutch retained in neutral while the main section is shifted to reduce inertia on the main section synchronizers and/or jaw clutches are also known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,974,906; 5,904,068; 5,661,998; 5,651,292 and allowed Ser. No. 09/346,381, the disclosures of which are incorporated herein by reference
While transmission systems utilizing such enhanced synchronizers and/or shift assist systems are effective to reduce the force required to shift a heavy-duty transmission, they also may permit engagement of ratios which are inappropriate for existing vehicle operating conditions.
The prior art also includes devices which will block inappropriate shifts (see U.S. Pat. No. 5,471,893 and WO 99/31409) and which will cause automatic range shifting as a function of vehicle speed (see U.S. Pat. Nos. 5,263,379 and 5,673,592).
These prior art devices were not totally satisfactory, as they were complicated and/or expensive and/or unduly restricted operator selection of ratios and/or could result in an undesirable transmission-neutral condition.